Coolant Temperature Sensor – How It Can Be Fixed?

Coolant Temperature Sensor – How It Can Be Fixed?

So, you have noticed something weird is happening to your car. Lately, you started gaining poor fuel economy, black smoke from the exhaust, overheating issue, and maybe even a check engine light? You probably think something really bad is happening with your car and you think of the worst, that it may die while you are driving, but you shouldn’t worry.

Some simple things may also cause this issue, simple as a coolant temperature sensor, which may be the culprit that you are looking for. If you see some of these symptoms happening you should probably consider checking out this sensor in order to get things done and make your car run properly.

Cars are packed with technology these days, and sensors are known to go bad more often than other parts. Sensors are parts that are sending information to your main ECU and then the computer basing on this information is deciding what to do in this situation.

If your sensors go bad especially the coolant temperature sensor. This sensor sends the engine incorrect information it may confuse the computer and make the car run badly. By running badly, I mean really bad. Usually, when a sensor breaks all kind of things can go wrong, bad idling, losing power, overheating, you name it.

So, if you see a check engine light on your dash, better pay a visit to your local mechanic and they will make sure that your car is fixed and you should be back on the road in no time.

But we are here to learn more and dive deep into this issue. To find out what is causing these troubles. We are going to get in the details and explain how this sensor works and also get into the ways you can diagnose it and also fix it by yourself because if you are reading this. You probably don’t want to pay mechanics for these easy fixes.

What is a Coolant Temperature Sensor?

The coolant temperature sensor, also known as the coolant temperature switch, this sensor purpose is to monitor the temperature of the engine’s coolant.

The coolant runs through the engine to keep your car at operating temperature and prevent overheating. And the coolant can also prevent freezing during the winter because the coolant is created for this specific purpose.

Many sensors are regulating the work of the engine and send the data to the ECU that is the main computer on the car. This computer then evaluates the signal and delivers constant adjustments to other components in the engine based on the new data.

Coolant temperature sensors are operating by using electrical resistance in order to measure the temperature of the coolant. Then this signal is sent to the ECU and the computer can make changes to the engine timing and also on the fuel calculations in order to get optimal performance.

It does this because engines require less fuel when they are warm and more fuel when they are cool. The main computer also will scale downgrade engine performance settings, if this coolant temperature sensor detects that the temperature in the engine is too high in order to prevent the engine from possible damage caused by overheating.

Overheating is a big issue for some engines, since they are prone to overheat, and these sensors are increasing the chance of overheating even more.

Imagine you run your car at high RPM alot and you are not aware that your sensor is bad, the car thinks the coolant temperature is normal and the fans don’t hook up when the vehicle goes above operating temperature and your engine will overheat, so address these issues with time.

Symptoms of a Broken Coolant Temperature Sensor

Temperature plays a very important role when it comes to engine performance calculations. If you have a broken coolant sensor, it will automatically translate into bad performance of the vehicle when hot. Usually, these symptoms are mild but if you notice them, you should be worried and take your car for inspection, or follow along with this article and learn more on how to check everything DIY.

These symptoms are a few, and we will list them below:

  • Poor fuel economy. This symptom is probably the worst, and one of the easiest to notice, because it will hurt your wallet and you will start asking yourself why is that so. Nevertheless, if the coolant temperature sensor goes bad, it will send false signals to the computer and it will cause a miscalculation in the computer when the computer measures the fuel timing. It is common for the coolant sensor to fail and send a permanently cold signal to the ECU. This will cause the engine to think that outside is cold and will throw in more fuel for the engine to burn than necessary. This is going to make engine performance go bad and fuel consumption will skyrocket.
  • Black smoke from the exhaust. This symptom is one of the possibilities that you will encounter when trying to find the issue. If you have black smoke running from your exhaust it means that something is wrong, but it can’t necessarily mean that the sensor is broken. Because there are also many other reasons for black smoke such as a broken catalytic converter. So, in this case, when the sensor is broken, it sends a permanent cold signal to the computer and makes the computer confused. And it may cause it to enrich the fuel mixture for no real reason. The mixture becomes too rich to be fully burnt in the combustion process and gets thrown out of the exhaust and it will burn inside it, causing huge clouds of smoke. Cases can be so severe that even police are going to stop you on the street and will prohibit you from driving this vehicle until is fixed.
  • Overheating engine. This is another common symptom that appears when the coolant temperature sensor goes bad. The sensor may fail in the opposite manner from the previous two cases and send a permanent hot signal. The car computer then may be confused and incorrectly compensate for a lean signal. This issue may cause your car to overheat and misfire. Overheating is a big issue and you probably don’t want it, since if it overheats it can warp your engine block and head and lead to permanent engine damage. So, if you suspect this issue it is better to visit your mechanic as soon as possible.
  • Check engine light on, in the previous article we discussed what causes check engine light and also flashing check engine light (such as the flashing check engine light in a Ford). This is also one of the potential symptoms of this coolant temperature sensor. The computer will fire off a permanent check engine light if it notices that something is wrong with the sensor’s signal or circuit. This light will stay on until the issue is resolved. If you are a beginner and not experienced with working on cars it is better to take your car to the local mechanic shop. If you think you are prepared for some troubleshooting, we have a special chapter for you and that will be for the purpose of getting this check engine situation resolved and the sensor replaced, so follow along.

My Car is Has Poor Fuel Economy, is This Sensor Related Issue?

Poor fuel economy may be caused by other reasons also. It doesn’t necessarily have to be a bad coolant temperature sensor. The most probable reason for this issue is bad fuel injectors. If your injectors are not working right, they can cause issues and ruin your fuel economy.

Another big reason is a clogged air filter. Filters should be changed regularly and your car should always run on a fresh filter in order to draw more air into the engine and make sufficient explosions in the combustion chamber.

Some of the other reasons why this is happening may be bad spark plugs, thick oil. And also some stupidly simple reasons like running your car on low tire pressure and if you are one of those guys that like to put their pedal to the metal and run the car on high RPM a lot, fuel consumption will suffer.

So how to differentiate this sensor fault from all of these symptoms? You can’t, you need your car to be properly inspected on a computer, or with an OBD scanner. We are going to discuss this more in the DIY chapter.

If I Have Check Engine Light, Does It Mean That My Sensor Is Bad?

If you are getting a check engine light it doesn’t necessarily mean that your sensor is bad. The check engine light may appear for many reasons. And one of them is the coolant temperature sensor. This sensor when it goes bad has specific symptoms that we mentioned above like increased fuel consumption, black smoke out of the exhaust, and overheating.

If you notice one of these symptoms and the check engine light you can be 80% positive that this is the culprit, also if you get one of these symptoms and no check engine light the sensor could still be bad. Because sometimes the check engine light does not fire up and you may think that your car is ok, but in reality, it is not.

Do your investigation first before you make conclusions, proper troubleshooting is essential when dealing with these issues and fixing them also.

As we mentioned before in another article there are two types of check engine light, flashing check engine light and fully light on check engine light. When this coolant temperature sensor is broken it is usually the second light. The light does not turn off when you have this issue.

Other issues on why you may have a check engine light that does not turn off may be caused by bad ignition coils (which you can diagnose by learning how to test ignition coil), bad fuel injectors, bad thermostat, catalytic converter failure, bad PCV valve, and this coolant temperature sensor (ETC sensor). All of these issues should be taken seriously and you shouldn’t drive your car as it is. Some of them are easy to fix, but some of them are needing serious attention.

If you cannot fix these issues by yourself, it is the best idea to take it to a professional and let them do all of the work.

Can Burning Oil Also Cause Black Smoke? And How to Differentiate This From The Sensor Issue?

Yes, it can cause black smoke, especially if it’s an older car and the piston rings don’t seal really well as they did 20 years ago when the car was new. But the question is how can you make a difference between a smokey car that is caused by a bad sensor and a smokey car that is worn out and burns oil?

Let me tell you it’s very easy to do that. If it’s the sensor the smoke should have a lighter color, which will be more blueish than black. Because oil is black the gas isn’t. When the oil burns it also smells really bad, unlike any gas car. Oil has a weird smell that reminds you of diesel cars rather than a gasoline vehicle.

That is a dead giveaway for you. Just observe the smoke and the color and give it a smell and you will know the difference between oil and unburnt gasoline.

Can a Bad Thermostat Also Cause Overheating?

Yes, it can, this is also one of the main things that will make you think that it’s the thermostat rather than a coolant temperature sensor. Because all the symptoms are there and they are pretty much the same. And the question is how to see if this is the sensor and not the thermostat?

Let me tell you… you cannot easily tell which one is the culprit. It just doesn’t go that way, either you replace the thermostat and hope for the best, or you decide to diagnose your car on a computer. You will spend money either way. But in my opinion, it is better first to replace the thermostat if your car overheats. These thermostats easily break and cause many overheating issues. Issues like coolant and oil can mix together and make a disgusting sludge in your engine and warp your engine and head. This may cause you to lose thousands of dollars for a new engine in the worst-case scenario.

On the other hand, these sensors do not go bad that often as the thermostats so that will be your second bet. If you replace your thermostat, just put your car on a computer and if you find a fault then replace the sensor right away. It may save you trouble in the long run and your engine will run perfectly well with no further issues.

Can I Fix This DIY?

This is the most important question that most of you were asking. And the answer is yes, you can fix this issue DIY with proper troubleshooting. Most of you as well as I do not like to go to mechanics and want to fix our cars by ourselves. Mostly because we do not like other people to touch our cars and also, we find pleasure doing this, learning a lot of cool stuff in the process.

The best thing about working on your own car by yourself is that you save money in the long run. You may spend some dollars on an OBD2 scanner but you will benefit in the future when other issues appear and you will have the proper diagnostics equipment on how to find and fix these minor issues.

coolant temperature sensor

So, let’s start and learn some new things on how to diagnose your coolant temperature sensor issue. If you have all of the symptoms mentioned above and you are still scratching your head on what may be the issue in this troubleshooting guide. We will address all of the situations that are possible for you to encounter:

  • The number one thing to do is to grab an OBD2 scanner tool, you can find these cheap on Amazon. They are inexpensive and can tell you a lot about your car. These scanners fit every vehicle no matter which make or model is. Just plug and play. The main difference among these devices is the amount of info and functionality they have. Starting from cheap ones that only allow you to clear of your codes, to expensive ones that will give you the ability to know how your car breathes. The second ones are also more expensive. They can cost a couple of hundred dollars and even more depending on the model that you plan to purchase. If you want to get seriously into this it is recommended to get a decent one, a good one will serve you for a long time.
  • Connect this scanner to the OBD2 port in your car, you can find these ports under the steering wheel, just look for it or if you want to take the easier route you can just google “where can I find my OBD port” and write the model of your car after that. Simple as that.
  • After you found your OBD port then turn on your car and connect your scanner to it, this is important because if the car doesn’t run it might not work.
  • After you connected it to your car, then run the scan, if your car is good, you won’t get any errors but if it’s broken you will get some that need to be addressed. These errors are usually some codes, and then you can use your cell phone to google them, if you found your coolant temperature sensor there, perfect. Go to your local parts shop and get the right sensor for your car.
  • Installing the sensor is an easy task, you only need a wrench to unbolt it and replace it with the new one. Here is also a video on how you can do it.
  • After you have done this, just erase all of the codes in your scanner tool and you are good to go. No more check engine light related to the coolant temperature sensor. And also, your car will say thank you buy running better and more efficiently with no black cloud of smoke from behind. Also, fellow drivers will not get angry at you for running your car like this in the traffic.

Can I sell a Car With a Broken Coolant Temperature Sensor?

That is a big question, you can sell it but when people see how it runs, they would like to stay away from it. Nobody likes a Christmas tree of check engine lights on their dash. Everyone who buys a car wants a properly running vehicle.

Also, if there isn’t a check engine light the smoke would be there and people that will come and see your car will think that it’s even something worse and the whole car is totaled. Even if they want to buy it, they will ask much less than you imagined to sell it for, so keep that in mind.

If it does not show a clear sign maybe someone would buy it, but it’s a bad practice to sell broken stuff to people, especially if you run a business, nobody will like to buy a vehicle from you again.

Fixing the car before you put it on the market would be a great idea, you will also get more money out of it and also the future owner would be happy with his new purchase.

Coolant Temperature Sensor Facts:

  • The coolant temperature sensor is responsible for monitoring the engine coolant’s temperature, and it uses electrical resistance to measure it accurately.
  • Temperature plays a crucial role in engine performance calculations, and a malfunctioning coolant temperature sensor can lead to engine performance hiccups.
  • Symptoms of a bad coolant temperature sensor include overheating engine, poor fuel economy, check engine light turning on, black smoke emitted from the engine, poor idling, and defective electrical cooling fans.
  • The coolant temperature sensor is often located on the cylinder head or engine block, installed conveniently on a plastic hose on the coolant’s inlet.
  • Some vehicles have two different temperature sensors for the fans, engine management, and dashboard gauge.
  • Diagnosing a malfunctioning coolant temperature sensor should be done by a certified technician, but vehicle owners can examine the engine component if they suspect it’s malfunctioning.
  • To diagnose a malfunctioning coolant temperature sensor, owners can compare the ohm value between the pins with the correct ohm-value in their repair manual and check the connectors and wirings between the sensor and the engine’s control module.
  • The coolant temperature switch is crucial to numerous calculations that ultimately affect the engine’s performance.
  • A malfunctioning coolant temperature sensor should be inspected by a professional or experienced technician to determine if a replacement is necessary.
  • If the coolant temperature sensor malfunctions, the computer may scale back engine performance settings to prevent overheating, which can damage the engine severely.


The coolant temperature sensor is vital in running a vehicle properly. If they are no good they may cause a series of issues like increased fuel economy, black smoke out of the exhaust, overheating issues, and more.

We found out what coolant temperature sensors are and what is their role and discussed many ways on how you can troubleshoot these issues. We also learned some mechanical DIY stuff that will get you back on the road in no time.

If you are interested in mechanical stuff don’t be afraid to work on your vehicle. By working on a car, you can learn a ton of useful and interesting things in the process. 

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